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https://github.com/aaru-dps/Aaru.Compression.Native.git
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79 lines
2.9 KiB
C
79 lines
2.9 KiB
C
/*
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* This file is part of the Aaru Data Preservation Suite.
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* Copyright (c) 2019-2025 Natalia Portillo.
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* Copyright © 2018-2019 David Ryskalczyk
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*
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* This library is free software; you can redistribute it and/or modify
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* it under the terms of the GNU Lesser General Public License as
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* published by the Free Software Foundation; either version 2.1 of the
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* License, or (at your option) any later version.
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*
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* This library is distributed in the hope that it will be useful, but
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* WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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* Lesser General Public License for more details.
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*
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* You should have received a copy of the GNU Lesser General Public
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* License along with this library; if not, see <http://www.gnu.org/licenses/>.
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*/
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#include <stdint.h>
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#include <string.h>
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#include "../library.h"
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#define DLE 0x90 // Data Link Escape character, used as a repeat marker.
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// Decompresses data using non-repeat packing.
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// This algorithm encodes runs of identical bytes.
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AARU_EXPORT int AARU_CALL arc_decompress_pack(const unsigned char *in_buf, size_t in_len, unsigned char *out_buf, size_t *out_len)
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{
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// Basic validation of pointers.
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if(!in_buf || !out_buf || !out_len) { return -1; }
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size_t in_pos = 0;
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size_t out_pos = 0;
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unsigned char state = 0; // 0 for normal (NOHIST), 1 for in-repeat (INREP).
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unsigned char lastc = 0; // Last character seen.
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// Loop through the input buffer until it's exhausted or the output buffer is full.
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while(in_pos < in_len && out_pos < *out_len)
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{
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if(state == 1)
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{ // We are in a repeat sequence.
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if(in_buf[in_pos])
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{ // The byte after DLE is the repeat count.
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unsigned char count = in_buf[in_pos];
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// Write the last character 'count' times.
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while(--count && out_pos < *out_len) { out_buf[out_pos++] = lastc; }
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}
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else
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{ // A count of 0 means the DLE character itself should be written.
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if(out_pos < *out_len) { out_buf[out_pos++] = DLE; }
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}
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state = 0; // Return to normal state.
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in_pos++;
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}
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else
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{ // Normal state.
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if(in_buf[in_pos] != DLE)
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{ // Not a repeat sequence.
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if(out_pos < *out_len)
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{
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// Copy the character and save it as the last character.
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out_buf[out_pos++] = lastc = in_buf[in_pos];
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}
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}
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else
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{ // DLE marks the start of a repeat sequence.
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state = 1; // Enter repeat state.
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}
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in_pos++;
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}
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}
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// Update the output length to the number of bytes written.
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*out_len = out_pos;
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// Return success.
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return 0;
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}
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